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Thread: Dreamcast Dedicated JAMMA mod (AV help needed)

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    Dreamcast Dedicated JAMMA mod (AV help needed)

    Hey guys,
    Not sure whether to slap this in Console mods (Since it is) or Arcade help (Since it also kinda is) so I'm going to leave it here.

    So I have a 'dead' Dreamcast that isn't displaying video.
    The TL;DR of it is a cheap Chinese replacement AV cable decided to rip pins out of the socket on it's way out of the console while packing it for storage.

    The system works besides no AV.

    So, since I have 3 units (1 JP-NTSC, 1 working PAL and the broken PAL in question) I have decided to hardmod this unit to run off JAMMA.

    The power I have sorted. I have decided to just pull power from the 12v line of the JAMMA harness via a PICO PSU replacement mod.
    I can also hard-wire control inputs to the JAMMA edge.

    What I need assistance with is the Video outputs.

    I need to remove the AV socket from the board and tap into the pins on the motherboard.
    Has anyone tapped into the RGB and sync off the motherboard for JAMMA before and able to offer some insight?

    Trying to gather pin-outs and advice on output frequencies and whether or not I'd need to add resistors etc as I want to run EVERYTHING off the JAMMA fingerboard without additional external converters.

    Any help would be greatly appreciated.

    As I gather parts and start work on this project I'll be sure to document and take photos/video of my work to hopefully make this easier if anyone else wanted to do the same.
    Updates may be slow on my part as I gather/prepare/build.

    Hope someone can help cheers guys.

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    Just an educated guess:

    Tap RGB and composite sync from the DC AV port.

    Tie pin 7 to ground to enable RGB mode from the DC.

    Run RGB through a video buffer such as a THS7316, you may need to add coupling caps to the inputs. On the outputs you'll want 75R's in series. You'll need a video buffer as the DC will be outputting 0.7V P-P whereas an arcade monitor will require 4V P-P. If the video amp isn't enough you may need to use additional pull-up resistors.

    I believe sync should be fine to pass straight through if you use the composite sync from the DC on pin 10, this should be a TTL level signal that'll work fine with arcade monitors.

    I'd imagine audio will need to be converted from line level to speaker level.
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    Sounds about right.
    Excuse my crappy draw up but I'm assuming this is what you mean.
    I have limited knowledge on some things so I'm unsure what you mean by 0.7V P-P and 4V P-P.

    MOD pins.jpg

    I own 2 of these fingerboards. I can use the built in space to the right to create my own audio amp/volume control to deal with the audio issue on-board.

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    That's the gist of it.

    To put it another way, the Dreamcast outputs low voltage video levels, designed to work with consumer TVs. Arcade monitors are very different beasts and require a high voltage video signal.

    So without any consideration for the video levels you'd end up with a very dim image on your arcade monitor. The RGB amp will remedy this and boost the RGB output of the dreamcast to arcade monitor levels.
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    Exellent. I'm aware the pins are wrong on that motherboard used for reference and it is indeed pin 7.
    I also have a VGA to CGA converter board. Was ordered accidentally while searching for CGA>VGA.

    I guess I could also activate VGA and use that converter board in place as well but I'd be running out of internal space if I did that.

    I'll have a decent amount of room since I'll be using a GDemu in place of the GDRom though it's nice to have options.

    While I'm at it and since I'll be removing the AV and serial ports as a whole (they're a single piece) I might as well just go ahead and also just wire up an SD reader directly to the serial port for dedicated Dreamshell access.

    As for controllers. I'll need to do more research. I have 2 donor madcatz digital controllers I can hack and mod but will look to see if it's possible to just pull inputs for controllers directly from the ports.

    Sent from my SM-G925I using Aussie Arcade mobile app

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    Let me know how it turns out. Dreamcast is a great console to run in an arcade.

    I'm more used to doing controls the other way around, as in go from console controller, demux the signal and spit out raw individual signals for jamma inputs. I'm guessing a pad hack will work for your needs, might be a little more involved than that though.
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    There are boards for doing what you are after. We used to use them when using Dreamcast inside arcade conversions. The board does plug into the Dreamcast but you could hard wire it and it has 3 pots for specifically adjusting the RGB levels. Also has an audio amp. Board does a few other things as well but they are more to do with coinage. Output of the board is jamma and off that you run joysticks, steering wheels, buttons etc.

    It was designed for simplicity when putting a console into an arcade. You plug the console leads into the board and jamma supplys the 12volt for the console. The jamma plug goes off to the rest of the machine.

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    Quote Originally Posted by Autosteve View Post
    There are boards for doing what you are after. We used to use them when using Dreamcast inside arcade conversions. The board does plug into the Dreamcast but you could hard wire it and it has 3 pots for specifically adjusting the RGB levels. Also has an audio amp. Board does a few other things as well but they are more to do with coinage. Output of the board is jamma and off that you run joysticks, steering wheels, buttons etc.

    It was designed for simplicity when putting a console into an arcade. You plug the console leads into the board and jamma supplys the 12volt for the console. The jamma plug goes off to the rest of the machine.
    Yeah I'm well aware of these boards.
    I'm just a fan of tinkering with things and making new things and trying to get it as self contained as possible. Cheers for the suggestion, they're just pretty expensive.

    Sent from my SM-G925I using Aussie Arcade mobile app

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    Ok, so RGB, composite sync, L/R audio has been tapped, and RGB selector has been bridged.
    TINY traces on board and unfortunately the contact pad for green has been burned out from solder side.

    I ran a coninuity check and all contacts are still working so crisis averted, I just tapped into the green from the AV connector pin on the parts side and ran it though a non important screw hole.

    Conviently, the pcb shield has holes all the way around it to asist with airflow.
    Since I'll be doing a PICO PSU mod as well, heat is less of an issue and I can get away with using them to route wires up and out the side to assist with making a clean link to the JAMMA edge.

    Also, since I'm using a GDEMU, I have space where the GDRom drive usually sits to build amps.

    It's a crued hack job at the moment but I see this as prototyping and practice and if I pick up another cast further down the line with a similar issue, I'll know exactly what to do.

    Progress pics so far, will continue when I get more parts along the line.
    20190302_153055.jpeg20190302_154042.jpeg20190302_154301.jpeg

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    Last edited by Cyber-dust; 16th March 2019 at 01:45 PM.

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    Was dumb... used short wires I had laying around. Extended and applied heatshrink sleeves, playing around with JAMMA edge location.

    The fingerboard I'm using has a space for prototyping. I'll need to cut it off.
    Once cut off, it can be reused for the RGB amp. The power-in socket will be obsolete once I have JAMMA power. Luckily the kit comes with a 3D printed socket housing. I can use this to plug the hole and use a dremel to extend the slot need for the JAMMA edge.

    I'll need to build a box to house the PCBS for my pad hack. Hopefully I can make something for the console itself to piggy back onto, house the PCBs in there and route wires to the JAMMA edge up through the bottom of the console. Standard controller cables out the front of the box and directly into the 2 ports on the console. Will at least make it look clean.

    On the inside I'll use some quick disconnect sockets for easy disassembly once I know everything works.
    20190302_173204.jpeg

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